Perception of Motion Complexity is Deficient in Adults with Autism Spectrum Disorder

Preference for biological motion is characteristic of typically developing children but not individuals with autism spectrum disorder (ASD) (Blake, 2003). However, this does not appear to be due to sensory deficit in individuals with ASD (Klin, 2009). Work in biomechanics has revealed that the kinematics resultant from biological sources of motion can be characterized by specific nonlinear measures of temporal structure of movement variability; i.e. entropy (Stergiou, 2003). In fact, health is related to an optimal state of this variability in movement over time. Contrastingly, stereotypic/rigid or noisy movements are not desirable. We hypothesize that the underlying deficit in the perception or identification of this variability may be characteristic of ASD, and the functional basis for the lack of discrimination of biological motion. Five adults without, and 2 with, ASD stood quietly on a force platform ( Accusway) viewing an oscillating point-light, driven either by sinusoidal (SN) or chaotic rhythm (CH). Postural sway and gaze (via eye-tracking) were collected for 60s; at 50 Hz. Sample entropy quantified the temporal structure of variability in each measure. Adults without ASD exhibited greater complexity of their gaze behavior towards the more complex motion (p=0.016), whereas adults with ASD did not differ in their gaze towards the two types of motion (p=0.544). Posture was not condition-responsive. We provide preliminary evidence that perception of structure of movement variability differs for adults with ASD when compared with adults without ASD; potentially related to the lack of preference for biological motion reported for individuals with autism.

Listed In: Biomechanical Engineering, Biomechanics, Neuroscience, Posturography

The effect of a random visual perturbation on git variability

Vision provides information about spatial location as well as other environmental features. Manipulation of visual input alters gait patterns including gait variability. When visual input was manipulated by a periodic change in the speed of optic flow, gait parameters showed a negative correlation with the speed of optic flow. Furthermore, step length variability increased when the optic flow was disturbed by discrete oscillations appearing at random time points. However, in this latter study the environment was horizontally oscillated without affecting the optic flow. No previous research has addressed how gait variability will be altered if the optic flow is perturbed randomly. Therefore, the purpose of this study was to investigate how gait variability changes during treadmill walking under two visual conditions: 1) random optic flow perturbations, and 2) normal optic flow. Ten healthy young adults (five males; aged 25±5 years) walked on an instrumental treadmill with a surrounding virtual reality environment. The coefficient of variation (CV; %) for step length and step time was used to assess gait variability. A pairwise t-test was performed to determine condition effects on step length and step time. The level of significance was set at 0.05. Our results confirmed that gait variability in both spatial and temporal aspects was affected by random visual perturbations. Our results showed that given random visual perturbation in both the amount and time of appearance reduced the gait variability. We speculated that stress played an important role to reduce the gait variability under random visual perturbations.

Listed In: Biomechanics, Gait, Posturography

Changes in Mechanical efficiency during repetitive hopping in long distance runners

INTRODUCTION: Mechanical efficiency(ME) may be a contributing factor in running performance. ME is the ratio between the amount of mechanical work performed and the amount of energy expended during exercise. PURPOSE: The purpose of this investigation was to determine the possible differences in ME and percent changes in ME with repetitive hopping between competitive and recreational long distance runners. METHODS: Nine male runners (age 20±1.05yrs; height 69.69±3.3in; weight 70±14.9kg) who ran at least 3 days a week were recruited. Participants reported to the lab on 2 days, separated by 1 week. On the first day, height, weight, and VO2max were measured. On the second day, participants completed 10 minutes of hopping on a force plate to determine ME. Subjects were classified as ‘recreational’ (Rec) or ‘competitive’ (Comp) based on their self reported 1600m time and their VO2 max (rec: VO2max<60.0 ml/kg/m, 1600 time≥5:00; com: VO2max≥60.0 ml/kg/m, 1600m time<5:00). RESULTS: The recreational group had a mean VO2max of 51.9±1.57 ml/kg/m, ME of 38.7±7.00%, and % change in ME of 29.9±16.6%. The competitive group had a mean VO2max of 64.1±3.8, ME of 43.29±9.45%, % change in ME of 14.6±5.17%. Percent change in ME between groups trends toward significance (p=0.14). A correlation was observed between VO2max and % change in ME that trended toward significance (r=-0.58, p=0.10). PRACTICAL APPLICATION: It appears that individuals categorized as competitive may maintain ME better than recreational runners (i.e. lower % change in ME). The ability to maintain ME during long duration stretch-shortening cycle exercise may be a factor pertaining to running performance.

Listed In: Biomechanics

A Novel Technique to Simulate Landing Biomechanics: a Cadaveric Model of ACL Injury

INTRODUCTION Acute ACL injury can be devastating, and often results in clinical sequelae including long-term disability and osteoarthritis. To study loading factors independently and in combination, such a model must be capable of consistent independent control of each parameter. We hypothesized that an unconstrained test configuration capable of independent application of loads about all anatomical axes of loading would allow us to evaluate each mode of loading separately an in combination, while generating realistic injuries patterns. METHODS 19 cadaveric legs (45±7 years) were tested under multiple combinations of anterior shear, abduction and internal rotation moments utilizing a novel drop stand. Landing was simulated by releasing either half or full body weight from 30 or 60 cm above the foot. Specimens were tested at 25o of flexion under simulated muscle loads. Joint kinematics and ACL strain were collected. RESULTS and DISCUSSION Our test setup was able to deliver a consistent impact load-time history. Experiments produced ACL failure in the majority of specimens. A clinically relevant distribution of failure patterns was observed. Detailed attention to impact parameters including mass, drop height and interface helped to generate an in vitro load-time history similar to in vivo data. This setup was designed to replicate the ranges of loading determined from in vivo studies of ACL injury mechanisms undertaken by our group. This evolution of experimental design facilitates the use of this experimental model to independently evaluate the effects of single and multi-axis loads on ACL injury, while recreating injury patterns observed in vivo.
Listed In: Biomechanical Engineering, Biomechanics, Sports Science

Grasp kinematics and kinetics during functionally-relevant tasks in healthy elderly individuals

The purpose of this study was to quantify the external moments and digit-tip forces acting on a freely moveable object while old (OA; 60-85 years) and young (YA; 18-50 years) adults performed functionally-relevant tasks. Able-bodied participants performed a grasp and lift task, and a precision-orientation (key-slot) task akin to inserting a key in the hole using a precision (thumb-index finger) grip. During the grasp-lift task the OA group misaligned their thumb and finger contacts, and produced greater grip force, greater external moments on the object around its roll axis, and oriented force vectors differently compared to the YA group. During the key-slot task, the OA group was more variable in digit-tip force directions and performed the key-slot task more slowly. With practice the OA group aligned their digits, reduced their grip force, and minimized external moments on the object, clearly demonstrating that the nervous system monitored and actively manipulated one or more variables related to object tilt. This was true even for the grip-lift task; a task for which no instructions regarding object orientation were given and which could tolerate modest amounts of object tilt without interfering with task goals. Although the OA group performed the key-slot task faster with experience, they remained slower than the YA group. We conclude that with old age comes a reduced ability to appropriately position their digits on an object, and then control the forces and moments applied to objects during precision grasp and manipulation. This may contribute to the ubiquitous slowing and deteriorating manual dexterity in healthy aging.
Listed In: Biomechanics, Neuroscience


Hitting performance has been highly correlated to bat swing velocity. Common practices use weighted implements immediately preceding hitting performance. Purpose: Therefore, the purpose of this study was to determine the influence of different weighted warm-up bats on 3-D bat swing kinematics. Methods: 22 recreationally trained college aged participants completed three warm-up conditions. Participants performed a self -selected warm up with a normal weight bat (NW); heavy weight bat (HW) or light-weight bat (LW) followed by 5 maximal swings within the 3-D capture volume and analyzed to assess swing kinematics. Results: A 2 x 3 RM ANOVA was used to analyze mean differences for maximum bat velocity (MBV), maximum back elbow extension (MEE), percent of swing at maximum bat velocity (%MBV), percent swing at maximum back elbow extension (%MEE) and bat velocity at maximum elbow extension (BVMEE). There was no significant (p > 0.1) interaction for sex in any variable, therefore, groups were collapsed. After collapsing, there was no significant (p > 0.1) differences in MBV following HW, LW or NW warm-ups. There were also no significant (p > 0.1) differences in %MBV, %MEE and BVMEE between any conditions. However, there were significant (p < 0.1) differences in MEE following HW, LW warm-ups. This was followed up with a LSD pairwise comparison demonstrating a significantly (p < 0.1) greater elbow angle in NW than HW warm-ups. Conclusion: These results indicate that warming up with different weighted bats has no effect on MBV, however there was a difference in overall kinematics.
Listed In: Biomechanics, Sports Science

Comparison of three lameness quantification methods using a model for presence and alleviation of forelimb heel pain in horses

Lameness is an important factor compromising equine performance. Research into lameness biomechanics is extensive, often based on induced lameness. To determine the effect of inducing and alleviating forelimb foot lameness on upper body movement, fetlock angle and ground reaction forces and to examine the necessary stride number to collect, vertical displacement of head, withers and os sacrum was measured in four horses trotting in a straight line. After inducing reversible forelimb heel pain via sole pressure (subjective grade 1-2/10), a palmar digital nerve block (PDNB) was administered. Baseline movement was compared to i) induced lameness, ii) PDNB administration with and without sole pressure and iii) PDNB having worn off. For each condition, subsets of randomly selected strides (n = 5-50) were compared to the ‘true’ mean (n = 60). Head movement detected induced lameness best. Alleviating lameness did not cause systematic movement changes. For mean trajectories within 5 mm of the ‘true’ mean, 15-30 strides were required. Our project compared for the first time changes to head movement, fetlock angle and vertical ground reaction forces following induced and alleviated forelimb lameness. Results showed that all three objective lameness measurements detected forelimb heel pain, with head movement showing greatest changes and peak vertical force mirroring fetlock angle. All three measures returned to baseline values following a palmar digital nerve block.
Listed In: Biomechanics, Gait

Influence of Handrail Use on Stair Walking Stability in Trans-Tibial Amputees

The ability to walk on stairs is an important skill, as stairs belong to the typical obstacles that can be widely found in most every environment. Various disabilities are known to reduce the stair walking efficiency in patients, which not only limits their range of mobility, but can also become a safety issue due to the high injury probability of stair accidents. Accordingly, the biomechanics of stair ascent and descent have been investigated to great extent. Previous studies that were conducted on different populations, including elderly people, patients having undergone ACL reconstruction, and amputees used force plates that were integrated in one or more steps of the stairs. This setup reduced the number of steps available for evaluation and limited information on step-to-step variability, a variable that indicates walking stability. Artificial limbs offer the opportunity to install sensors to directly measure forces and moments in the weight bearing structure of the locomotor apparatus, which allows continuous data collection over entire flights of stairs. This poster presents preliminary findings on stair walking kinetics in trans-tibial amputees, as part of a larger, ongoing study of lower extremity kinetics of amputee gait
Listed In: Biomechanics, Gait, Orthopedic Research, Other

Effects of Increased Step Width on Frontal Plane Joint Mechanics in Older Adults During Stair Descent

The purpose of this study was to examine the effects of increased SW on GRF and lower limb joint motion in healthy older adults during stair descent.Eight healthy older men (52.1 ± 7.4 years, 75.7 ± 10.0 kg, 1.75 ± 0.09 m) were recruited for the study. An instrumented 3-step staircase (FP-stairs, AMTI) mounted independently to two force platforms (1200 Hz, AMTI) with two additional customized wooden steps (4th and 5th steps) was used to collect GRF data during stair descent trials. Participants performed five stair descent trials at their pre-established self-selected speed at self-selected, wide, and wider SW. Loading rate of impact peak vertical GRF and peak medial GRF were greater with wider SW compared to normal and wide SW. Peak ankle eversion angle was reduced with increasing SW and peak ankle inversion moment was smaller in wider SW compared to normal and wide SW. Peak hip adduction angle was greater in wider SW while peak hip abduction moment was smaller in wider SW compared to normal and wide SW. More healthy participants will be tested to increase sample size. Older adults with medial compartment knee osteoarthritis (OA) are also currently being tested to compare the effects of increased SW on GRF, and lower extremity joint variables to healthy adults during stair descent.

Listed In: Biomechanics, Gait

Abnormal isometric trunk kinetics observed in chronic stroke may be due to asymmetrical activation of extensor muscles

INTRODUCTION: The only quantitative studies regarding the impairment of the trunk after stroke have focused on strength measures in a single plane. The aim of this study was to quantify and identify differences in primary and secondary trunk kinetics in chronic stroke subjects during the generation of a maximum isometric torque. METHODS: Using a custom-built device with a 6-DOF load cell, multi-directional isometric trunk control of 14 stroke and 14 control subjects were evaluated in a seated posture. Subjects performed maximum voluntary efforts of trunk torque in 6 directions. EMG electrodes were placed on seven pairs of trunk muscles. Visual feedback of the intended torque (primary torque) was displayed to the subject. All other torques (secondary torques) were not shown. RESULTS: The stroke group generated larger axial torque towards the paretic side when compared to the non-paretic side, wherein the control group did not differ between sides. The stroke group coupled non-paretic axial torque during trunk flexion and paretic axial torque during trunk extension. During torque generation in the sagittal plane, the stroke group had larger activations and greater asymmetries in the trunk extensors. This suggests inefficient or abnormal trunk control as opposed to weakness of trunk musculature which will contribute to trunk discoordination. DISCUSSION: Differences between groups in secondary trunk coupling were observed during primary torque generation in the sagittal plane –a task that required symmetrical control of both sides of the trunk. CONCLUSION: Hemiparetic stroke may result in a more lateralized deficit in trunk control than previously thought.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Neuroscience, Physical Therapy